Immunity to Helminth Infections

Abstract

Vaccination with irradiated Trichostrongylus colubriformis larvae gave over 90% protection in mature sheep in pen studies, in which challenge with normal infective larvae was given either by impulse (a single large does of larvae) or sequentially (frequent smaller doses administered orally over a period of four weeks). Sequential challenge was designed to simulate the type of exposure to infective larvae likely to be encountered in the field. Vaccination was highly effective whether challenge infection was superimposed on the worm burden developed from the irradiated larvae or given after removal of the vaccine worm burden by anthelmintic treatment.